The invention relates generally to heating devices that rely on the combustion of high pressure gaseous fuels such as liquid petroleum gases or high pressure natural gas, particularly where portability is important such as with a heat gun.
Numerous heating applications in home and in industry require a heat gun as a high velocity source of moderately hot air. For example, direct heating of objects in processes such as paint removal or shrink wrapping plastics require moderate temperature to avoid charring or overheating while high velocity enhances heat transfer.
A conventional heat gun relies on electrical fans to move the air heated by combustion of fuel gas. The drawback of these devices is the added weight of the electrical motors and inability to use these units in the field where electricity is not available.
A different, commercially highly successful heat gun is described in a previous patent of Zagoroff, a coinventor of the current invention, U.S. Pat. No. 3,779,694, HEAT GUN, granted Sep. 23, 1973. The fuel jet pressurizes combustion air in a jet pump, feeding the mixture into an internal combustor. In the combustor, the gases expand by the addition of heat of combustion and exit as a high velocity jet of exhaust gases at stoichiometric burning temperature of over 3000.degree. F. and discharge velocities exceeding 4000 feet per minute. This jet entrains and propels copious amounts of ambient air in a second jet pump to create a blast of heated air at moderate temperatures. By virtue of the combustion at elevated pressure, a portion of the combustion energy of the fuel is converted to mechanical energy of the exhaust gases which augments the power available to pump air in the secondary jet pump.